In general, in a case of coating vehicle bodies of automobiles, articles of furniture, electrical appliances, and the like with paint, a rotary atomizing head type coating machine that is excellent in a coating efficiency and coating finish of paint is used. The rotary atomizing head type coating machine is provided with an air motor that uses compressed air as a power source, a hollow rotational shaft that is rotatably supported by the air motor and a tip end of which projects to a front side from the air motor, a feed tube that extends to the tip end of the rotational shaft through in the rotational shaft to supply paint or wash fluid, a rotary atomizing head a base end side of which is formed of a cylindrical section mounted to the tip end of the rotational shaft and a portion closer to a front side than the cylindrical section of which is formed of a cup section enlarged in a cup shape to spray paint from a tip end of the cup section, a shaping air ring that is arranged on an outer peripheral side of the rotary atomizing head, has a ring inner peripheral surface facing an atomizing head outer peripheral surface of the rotary atomizing head with a clearance, and has many shaping air spurting holes on a front end surface to spurt shaping air, and assist air spurting holes that are provided to open to the ring inner peripheral surface of the shaping air ring and spurts assist air into an annular clearance defined between the ring inner peripheral surface and the atomizing head outer peripheral surface of the rotary atomizing head.
Here, in the rotary atomizing head type coating machine, a large part of paint particles in the paint particles sprayed from the rotary atomizing head fly toward the object to be coated by the shaping air spurted from each of the shaping air spurting holes in the shaping air ring. However, a part of the paint particles sprayed from the rotary atomizing head flows around the rotary atomizing head and enters into the backside thereof, and the paint particles having entered into the back side adhere to the atomizing head outer peripheral surface.
Therefore, the rotary atomizing head in the conventional technology is provided with a solvent passage (wash fluid passage) for guiding the wash fluid onto the atomizing head outer peripheral surface from the cup-shaped inner peripheral surface. At the washing work, a part of the wash fluid ejected onto the cup-shaped inner peripheral surface from the feed tube is guided through the solvent passage onto the atomizing head outer peripheral surface, and the paint particle having adhered to the atomizing head outer peripheral surface is washed by this wash fluid (Patent Document 1).